The invention relates to a process for producing a liquid-solid metal alloy phase for further processing as material in the thixotropic state, wherein an alloy melt having a solidified portion of primary crystals is maintained at a temperature between solidus and liquidus temperature of the alloy, and the primary crystals are molded to give individual degenerated dendrites or cast grains of essentially globular shape.
It is known to set the temperature of an alloy melt to a value between solidus and liquidus temperature in the production of metal alloy phases having thixotropic properties, and to stir the alloy paste thus produced vigorously to convert the dendrites forming during the solidification process to give essentially globular cast grains. This process and the possibilities for use of the metal alloy phase having thixotropic properties thus produced is described in detail, for example in U.S. Pat. No. 3,948,650 and U.S. Pat. No. 3,959,651. The stirring effect is produced mechanically or electromagnetically. German Patentschrift 2 514 386 also discloses a process in which an alloy in billet or rod form is heated to a temperature between liquidus and solidus temperature and is maintained for a few minutes to hours at this temperature without stirring.
However, the three processes mentioned have considerable disadvantages. There is the danger for both mechanical as well as for electromagnetic stirring that, on the one hand oxide skins which form on the surface of the melt, and on the other hand air bubbles produced by vortex formation are stirred into the melt, and this is manifested in the end product by undesirable inclusions or porosity. In addition, a uniform cast grain size cannot be achieved using the two processes. Furthermore, effective stirring in the region of the solidification front of the alloy paste can only be implemented with difficulty using a mechanical stirring device for reasons relating to construction. The disadvantages caused by stirring may indeed be reduced in the process according to German Patentschrift 2 514 386, however, undesirable grain coarsening occurs due to the relatively long holding time of the alloy paste above solidus temperature.